Radiation of polymer materials as a method of chemical processing is known in the art. For example, Bohm and Tveekrem, "The Radiation Chemistry of Elastomers And Its Industrial Application", Rubber Chemistry and Technology, vol. 55, 575-668, discuss the effect of radiation of elastomers, such as ethylene-propylene copolymers and terpolymers; and Harmer and Ballantine, "Applying Radiation to Chemical Processing", Chemical Engineering, 91-98, May/ 1971 which describes various types of radiation.
The irradiation of elastomers, such as ethylene-propylene copolymer rubbers or ethylene-propylene-diene terpolymer rubbers is a viable method, or alternative, for crosslinking said materials, as described in O'Donnell and Whittaker, "The Radiation Crosslinking and Scission of Ethylene-Propylene Copolymers Studied by Solid-state Nuclear Magnetic Resonance", British Polymer Journal, vol. 17, no.1, 51-55, 1985. The crosslinking of elastomers is desirable in fabricated parts. U.S. Pat. No. 4,170,664 describes a process for the production of cross-linked resilient automotive body components having a cured surface coating from a thermoplastic elastomeric composition.
It is also known that by irradiating normally solid, linear, C.sub.2-4 alpha-olefin homopolymers and random copolymers of propylene with ethylene and/or C.sub.4-8 alpha-olefins, according to the processes of U.S. Pat. Nos. 4,916,198, 5,047,446 and 5,047,485, polymers are obtained having high melt strength or strain hardening (an increased resistance to stretching during elongation of the molten material) without crosslinking and gelation.
However, when irradiated C.sub.2-4 alpha-olefin homopolymers and random copolymers of propylene with ethylene and/or C.sub.4-8 alpha-olefins are blended with irradiated or non-irradiated elastomers to obtain better impact strength, the melt strength suffers.
The irradiation of heterophasic resins by conventional radiation methods has resulted in a heterophasic resin having melt strength, but severe gelation and high degree of crosslinking, which are undesirable in foam applications.
Thus, there is a need for high rubber heterophasic resins having good melt strength without substantial gelation or a high degree of crosslinking.